The primary objectives of the study are to evaluate the toxicities associated with Levulan®-mediated photodynamic therapy in pre-malignant head and neck lesions, and to evaluate the toxicities of continuous vs. fractionated light treatment. The secondary objectives are to assess the efficacy of Levulan®-mediated photodynamic therapy in pre-malignant head and neck lesions, and to assess the efficacy of fractionated versus continuous light treatment.